CGPathExtensions.cs

using System;
using System.Runtime.InteropServices;

namespace MonoMac.CoreGraphics
{
	public static class CGPathExtensions
	{
		[DllImport (Constants.CoreGraphicsLibrary)]
		static extern IntPtr CGPathCreateMutableCopy (IntPtr source);
	
		[DllImport (Constants.CoreGraphicsLibrary)]
		static extern void CGPathRelease (IntPtr source);
		
		[DllImport (Constants.CoreGraphicsLibrary)]
		unsafe static extern IntPtr CGPathCreateCopyByStrokingPath (
			IntPtr path,
			CGAffineTransform *transform,
			float lineWidth,
			CGLineCap lineCap,
			CGLineJoin lineJoin,
			float miterLimit
		);

		public unsafe static CGPath CopyByStrokingPath (this CGPath path, CGAffineTransform transform,
			float lineWidth, CGLineCap lineCap, CGLineJoin lineJoin, float miterLimit)
		{
			var copy = CGPathCreateCopyByStrokingPath (path.Handle,
				&transform, lineWidth, lineCap, lineJoin, miterLimit);

			// this will call CGPathRetain, which we don't want
			var mutable = CGPathCreateMutableCopy (copy);
			CGPathRelease (mutable); // so immediately release it

			CGPathRelease (copy);

			return mutable;
		}
	}
}